Here's a set of NPC replacement outfits so you can create your very own STFU.

STFU Llamas

I have not done anything to the Cow mascot, since it doesn't have any logo on it to begin with.I also have a bunch of (non-replacement) STFU t-shirts and other clothes, but the textures need some work, so I'm not uploading those at the moment.

Can you tell me where you found a tutorial to do default replacements or how to do it, please?

Windkeeper's tutorial helped me. I had to improvise a bit since the original outfits are hidden, but other than that the tutorial is easy to understand.I tried the NPC replacer from Simwardrobe , but it didn't have the llama mascot or the SS members, and the packages it makes are not entirely stand-alone.

For the record, the llama mascot outfits also replace the mascot outfit from the athletics career.

I was thinking of what Pescado said, and I also sort of wish I could do more with the original roman helmet mascot.So I made this Secret Society outfit. I think I like this better, but some people might miss the blatant lack of subtlety of the STFU-trxt, so I'll call this an alternate version.

That armour is good enough for this purpose, but the original Llama costume works for both genders and ages teen to elder, using the same mesh and textures for all ages and genders.I wouldn't be able to replace it with anything other than a mesh with those same properties, and I'm not likely to find any mesh that does all that.